High speed downlink packet access (HSDPA) was introduced in Release 5 of the third generation partnership project (3GPP) specifications in order to provide high data rates in the downlink to packet data users in a universal mobile telecommunications system (UMTS). These high data rates may be achieved by increasing the spectral efficiency using concepts such as adaptive modulation and coding (AMC), fast physical layer retransmissions such a hybrid automatic repeat requests (H-ARQ), and fast scheduling for base stations called Node Bs.
In an HSDPA system, there can be occasions when a user equipment (UE) transitions from one cell to another. This transition is referred to as a handover. It is desirable during a handover to maintain cellular communication without interruption. In an HSDPA system, a UE may monitor a high speed shared channel in a single cell, or a “serving HS-DSCH cell”. During handover, the UE transitions from communicating via a “source” Node B to a new serving HS-DSCH cell, (e.g., target cell/Node B). This procedure is referred to as a serving cell HS-DSCH cell change. However, HSDPA does not support soft or softer handover, where the UE simultaneously receives downlink data from multiple cells, i.e. multiple Node Bs.
In order to support the handover process, the UE continuously monitors the signal strengths of the serving cell and neighboring cells. Once the signal strength measured on the monitored reference channel of a neighboring cell exceeds the signal strength of the serving cell, the UE may signal to a radio network controller (RNC) associated with one or more of the Node Bs that a change of best cell event has occurred. This may be reported via a radio resource control (RRC) “MEASUREMENT REPORT event 1D” that contains the measured value and the cell identification (ID).
Upon the receipt of the RRC MEASUREMENT REPORT event 1D, the serving RNC (SRNC) determines whether or not to perform a handover to a new cell. The SRNC request the controlling RNC (CRNC) to allocate HS-DSCH resources, (e.g., HS-DSCH radio network temporary identifier (H-RNTI), high speed shared control channel (HS-SCCH) codes, HARQ resources, and the like) for the UE in the target cell. This may be performed via radio network subsystem application part (RNSAP) or Node B application part (NBAP) messages. Once the resources are reserved, the CRNC provides information to the SRNC, which transmits an RRC handover message to the UE that includes the radio access parameters required for the UE to begin monitoring the target cell. The RRC handover message may also include an activation time for the handover to take place.
Since the RRC handover message is sent to the UE via the source Node B over the high speed shared channel, a delay that is associated with the HS-DSCH serving cell change procedure may cause a failure of the RRC handover message transmission. Consequently, the rate of dropped calls may increase. In order to address this issue, it has been proposed to transmit a handover command in the target cell or in both the source and target cells, since the UE may be closer to the target cell when the handover situation is imminent. However, there is currently no ability to send feedback information for more than one cell at a time, which the inventors have recognized may cause unreliability and poor performance issues where the RRC handover message is transmitted in more than one cell. Additionally, with feedback being limited to a single cell, UEs that are designed to receive data from more than one cell at a time may perform less than optimally.
It would therefore be beneficial to provide a method and apparatus for feedback signaling.